Refrigeration can substantially reduce the rate at which food will deteriorate, since low temperatures slow down the growth of microorganisms contained in food.
Refrigeration has a long history, from prehistoric times to industrialization. Designs are driven by requirements to control bacterial growth, which are effected by temperature acting over time.
The invention of fridge compartments arising from the need to store perishables over different temperature ranges and humidity, has added versatility in storing food types, and therefore safety in eventual consumption. However, food spoilage is still a reality if recommended food storage times are not observed.
Slow Evolution to Refrigeration
Early man found that keeping his prized game stored in the coolness of a cave or packed in snow would make his food last longer. With the advent of industrialization, humans learned to mechanize ice by harvesting from lakes and rivers during winter and storing in “icehouses” for later distribution (Fig. 1).
A long, slow evolution to modern mechanical refrigeration can be traced as a culmination of human endeavour in last quarter of the 19th century. The new technology consisted of a compressor together with refrigerant fluid installed in an upright metal container with compartments and a door for easy access by consumers in every home.
Bacteria and Storage Temperatures
Bacteria exist everywhere in nature: in the soil, air, water, and in the food we eat. Bacteria grow most rapidly in the temperature range between 5°C and 45°C (40°F and 140°F), the so-called "Danger Zone," where some doubling in the number of bacteria can occur in as little as 20 minutes.
Refrigeration is well-known to counter bacterial growth and slow it down. Figure 2 is an empirical graph showing a set of temperature-time curves for the storage of various foods: butter, meat, fresh fish and milk. To highlight important variations, a focus is made on two different foods at two different temperatures, for example:
- Fish will store for 10 days at 0°C but is extended to 60 days at -15°C
- Meat stores for 20 days at 0°C but for up to 12 months at -15°C.
Clearly, for given types of foods that can be frozen, the cooler temperatures have a dramatic effect on the storage time.
Refrigerator Compartments Needed
As different foods were found to need different storage temperature ranges and humidity, four separate compartments were made available to consumers:
- Freezer, -18°C (0°F)
- Meats, 0°C (32°F)
- Main refrigerator, 5°C (40°F)
- Vegetables, 10°C (50°F)
Very often, storage of vegetables is complicated by the need for careful ventilation to remove unwanted gases and avoid humidity conditions, which would spoil the produce. Relative humidity requirements vary depending on the moisture content of the produce.
Food and Refrigerator Tips
It is important that a thermometer be used to check if a refrigerator is working properly at 5°C or below. The fridge and freezer doors should not be used more often than necessary; they should be closed tightly at all times and as soon as possible.
Food buying safety tips involve checking that foods brought home for the fridge contain a minimum of bacteria to start with. Good practice is to keep the fridge clean and free from odors and check food storage tables (or charts) to ensure stored food does not exceed the recommended times. It is stressed that not adhering to these safe time limits will pose a risk to foods becoming dangerous to eat.
Harry P. Schlanger - Hello, I started out as a physicist working for research organisations. Mostly in the area of heat transfer in solids and porous media. ...
